1. Field of the Invention
The present invention relates to an optical recording medium such as an optical disc recorded with information signals and a recording method therefor, particularly, relates to an optical recording medium of which a track is formed in a main information recording area on a disc shaped substrate, wherein the track is formed in concentric circles or in a spiral composed of array of a plurality of pits, and wherein tracks adjoining to each other are arranged approximately in a same pitch.
2. Description of the Related Art
With respect to contents of information recorded in an optical recording medium such as an optical disc, there provided prior arts related to express or indicate visibly numbers or characters such as alphabet indicating a recognition number or a manufacturing sequence number, which is inherent to the optical recording medium itself, and related to display visibly a design pattern corresponding to a content of information recorded. Actually, various methods or systems have been realized.
In order to prevent information signals such as music, video image or game software recorded in an optical disc from illegal duplication by illegal operation or reverse engineering, there provided prior arts disclosing a recording method, which records information of verifying that the optical disc is a genuine optical disc or a legally manufactured optical disc, wherein the verifying information is recorded as information by a visible character or symbol or pattern, or as information, which can be read out as data by utilizing pits allocated on a track. Actually, various systems or methods of preventing information signals from illegal duplication have been utilized.
The prior art, for example, Japanese Patent Laid-open Publication No. 58-100235/1983, which is filed by the same applicant as that of the present invention, discloses that numbers or characters such as alphabet indicating a recognition number or a manufacturing sequence number inherent to an optical disc itself and patterns related to a content of recorded information are recorded outside an information recording area, which is an area for recording information originally to be recorded such as music or video images, wherein such numbers, characters or patterns are visibly displayed or indicated by a dot pattern, which is formed a same pit structure as a pit recorded with information originally to be recorded as mentioned above.
The other Japanese Patent Laid-open Publications such as No. 9-128809/1997, No. 8-83440/1996 and 9-115186/1997 provide methods of forming an inherent pattern outside an information recording area of an optical disc. According to these methods, characters and patters can be displayed or indicated visibly in a main information recording area of an optical disc. Further, it is advantageous to an optical disc that characters or patterns can be formed on the disc during the same manufacturing process of recording information such as music or video images originally and can be displayed or indicated.
However, in all these methods, an exclusive pattern for indicating characters or designs is formed by exclusive pits for displaying the characters or the designs, wherein the exclusive pits are a different format from pits for information to be recorded originally. Accordingly, such exclusive pattern for indicating characters or designs can be displayed only in a narrow area such as a blank space outside an information recording area for recording information to be recorded originally. In other words, there exist a problem that it is basically impossible to indicate characters or designs at an arbitrary location in an information recording area of an optical disc and in arbitrary dimensions.
On the other hand, Japanese Patent Laid-open Publications No. 7-130134/1995 and No. 8-273201/1996 provide a method of forming a pattern for visible characters or designs in an information recording area as well as outside an information recording area.
The Japanese Patent Laid-open Publication No. 7-130134/1995 discloses that a pattern for visible characters or designs are formed with pits in an information recording area of an optical disc in conjunction with information to be recorded originally by writing the information to be recorded originally and the pattern for characters or designs in the CAV (Constant Angular Velocity) and CLV (Constant Linear Velocity) systems respectively. According to the disclosure, a pattern for characters or designs is formed with a pit of the CLV system on an optical disc, wherein information such as music and video images are originally recorded with a pit of the CAV system. Accordingly, a pattern for visible characters or designs can be displayed in an information recording area of an optical disc in conjunction with recording information to be recorded originally.
Forming information to be recorded originally and a pattern for indicating characters or designs in one recording area by writing them with the CAV and CLV systems respectively is assigning some of pits, which are originally provided for recording information to be recorded, to the pattern for indicating characters or designs. In other words, some pits out of a total capacity of pits provided for the information to be recorded in the recording area are utilized for forming the pattern for indicating characters or designs. Accordingly, recording capacity for the information to be recorded originally in the recording area is sacrificed for the pits assigned to the pattern for indicating characters or designs.
Since a pattern for indicating characters or designs can be formed in one recording area together with information to be recorded originally by these prior arts, it is possible to display the pattern for indicating characters or designs at an arbitrary location and in arbitrary dimensions. However, there exists a problem that recording capacity for the information to be recorded originally is decreased by recording capacity for the pattern for indicating characters or designs. The problem is rather serious problem for an optical disc, which is recently required to increase its recording capacity. In other words, the prior arts mentioned above can not comply with such a requirement that information to be recorded originally such as music, video images and application software shall be recorded as much as possible in an optical recording medium like an optical disc. It is disadvantageous to the prior arts.
The other prior art related to forming a visible pattern of characters or designs in a recording area is disclosed in the Japanese Patent Laid-open Publication No. 8-273201/1996. According to the disclosure, in a dual disc such as a DVD (Digital Versatile Disc), which is a disc having a structure of sticking two transparent substrates together, a pattern for indicating characters or designs is displayed in a main information recording area of the dual disc by interposing the pattern for indicating characters or designs printed, for example, in between the two transparent substrates.
However, this prior art can not be applied to an optical disc having only one transparent substrate, that is, an optical disc having single layer of transparent substrate, because the art is applied only to an optical disc having dual layers of transparent substrate.
Japanese Patent Laid-open Publications No. 8-212560/1996 and No. 61-123026/1986 provide another method of writing information for identifying an optical disc whether it is a genuine or fake as a symbol or cipher on a data array or signal not as a visible pattern. Such symbol or cipher can be identified as data and further the information for identification can be protected from duplicating illegally by the method. Therefore, it is possible to identify whether the optical disc is a genuine or fake more accurately and also it prevents an optical disc from illegal duplication, and the illegally duplicated optical disc can be securely identified.
If the art is practiced, however, it causes a problem that an exclusive apparatus for writing and reading out data for identifying an optical disc whether a genuine or fake must be furnished. Further, there exists another problem that the optical disc can not be identified whether it is a genuine or fake at a glance unless the apparatus is utilized. In addition thereto, it is essentially impossible to display characters or designs visibly.
As mentioned above, the prior art, which displays a visible pattern of characters or designs by utilizing a regular pit for recording information, has an advantage of being able to obtain the visible pattern through a simple manufacturing process because the visible pattern for displaying characters or designs can be formed by utilizing a same pit as that for recording original information. However, an area in where such a visible pattern can be displayed is limited to a narrow area outside the original information recording area such as an outermost circumference area or an innermost area of an optical disc, that is, an extra space area. In addition thereto, only characters or designs in small dimensions can be displayed in the narrow area.
In the case of the prior art of displaying a visible pattern such as character and design in the original information recording area, since some pits in the information recording area are diverted to the visible pattern, the pits are no more utilized for recording original information. Accordingly, recording capacity for recording information to be recorded originally is decreased and it causes a problem of being against a recent market demand for increasing information recording capacity much more.
Pits for recording original information together with pits diverted to the visible pattern are mixed in the information recording area of an optical disc, it is necessary for a reproducing apparatus to discriminate two types of pits one by one when the optical disc is loaded into the apparatus and the original information is read out. The apparatus must be equipped with a function of discriminating types of pits rapidly and accurately one by one, otherwise the pits diverted to the visible pattern may be read out as noise or irregular data. Accordingly, it causes problems that the recorded information can not be reproduced accurately and that the original information can be reproduced as music, video images or application software including many noise or irregular data.
In the case of utilizing the visible pattern mentioned above as an identification symbol for preventing an optical disc from illegal duplication, since recorded contents of the disc and the visible pattern can easily be reproduced by a regular reproducing apparatus if the visible pattern is formed by the same forming system as that of general pit. Such the identification symbol is actually not effective to prevent the optical disc from or to find illegal duplication or reverse engineering. Accordingly, it is necessary to form an identification symbol for preventing an optical disc from illegal duplication by the other forming method or system.
There existed another problem that a sophisticated apparatus exclusively for writing or reading out identification data must be prepared although the prior art of writing or reading out an invisible symbol or cipher as an identification symbol or identification data for preventing an optical disc from illegal duplication is provided. It is impossible to confirm an optical disc whether it is a genuine disc or faked at a glance, unless such the apparatus is utilized. In addition thereto, it is essentially impossible to display characters or designs visibly, because they are recorded invisibly as data.
Accordingly, an object of the present invention is to provide an optical recording medium, which solves problems in the prior arts mentioned above.
In order to achieve the above object, the present invention provides an optical recording medium such as an optical disc, which can display a visible pattern such as characters or designs at an arbitrary location in a main information recording area on a substrate of the optical recording medium and can maintain original recording capacity sufficiently without loosing any recording capacity for information to be recorded originally although means for displaying a visible pattern are provided in the information recording area. Further, the optical recording medium is equipped with means for displaying the visible pattern such as characters or designs, which can be apparently identified visually at a glance and utilized as an identification pattern being not able to be duplicated illegally.
According to an aspect of the present invention, there provided an optical recording medium comprising tracks, which are arranged in concentric circles or a spiral on a disc and composed of plural pits, wherein a track pitch between adjoining tracks is formed approximately equal to each other, the optical recording medium is recorded with an information signal by means of the plural pits, the optical recording medium is further characterized by that the track pitch is displaced to a radial direction of the disc in response to a desired pattern of character and/or design, and that the desired pattern is displayed visibly at least in a recording area for the information signal of the disc by an interference of a reflected light caused by a displaced track pitch, wherein the interference caused by the displaced track pitch is different from other interference of a reflected light caused by a track pitch not displaced.
According to another aspect of the present invention, there provided a recording method of an optical recording medium having tracks, which are arranged in concentric circles or a spiral on a disc and composed of plural pits, wherein a track pitch between adjoining tracks is formed approximately equal to each other, said optical recording medium is recorded with an information signal by means of said plural pits, the recording method further comprises a step of displacing the track pitch to a radial direction of the disc in response to a desired pattern of character and/or design and a step of displaying the desired pattern visibly at least in a recording area for the information signal on the disc by an interference of a reflected light caused by a displaced track pitch, wherein the interference caused by the displaced track pitch is different from other interference of a reflected light caused by a track pitch not displaced.
Other object and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.